Fix #1671 by ignoring mouse ups on flyout buttons when there is a drag in process.
Fix #1671 by ignoring mouse ups on flyout buttons when there is a drag in process.

This issue was caused by adding pointer-events:none on the drag surface 
element in https://github.com/LLK/scratch-gui/pull/2584

LLK/scratch-blocks,LLK/scratch-blocks,LLK/scratch-blocks,LLK/scratch-blocks,LLK/scratch-blocks